Conventionally, there is known a hybrid engine-driven power generator including a rectifier for converting an AC 3-phase output voltage from an alternator driven by an engine into a DC voltage, an inverter for converting the DC output of the rectifier into an AC output voltage, a filter circuit, a battery, a DC/DC converter for boosting a DC voltage of the battery and supplying the same between the rectifier and the inverter, and a control part for controlling the outputs of the inverter and the DC/DC converter. The hybrid engine-driven power generator of this type is described in Japanese Patent Publication No. 3941927, for example. Japanese Patent Publication No. 4082657 describes therein, for example, a structure of the hybrid engine-driven power generator in which the DC voltage of the battery is boosted and supplied to the DC/DC converter during an overload while when an external load current is larger than a rated current value, the voltage of the inverter is changed according to a preset map.